Conventional golf balls can be divided into two general types or groups: solid balls or wound balls. The difference in play characteristics resulting from these different types of constructions can be quite significant.
Balls having a solid construction are generally most popular with the average recreational golfer because they provide a very durable ball while also providing maximum distance. Solid balls are made with a solid core, usually formed of a crosslinked rubber, which is encased by a cover material. Typically the solid core is formed of polybutadiene which is chemically crosslinked with zinc diacrylate and/or similar crosslinking agents and is covered by a tough, cut-proof blended cover. The cover is generally formed of a material such as SURLYN, which is a trademark for an ionomer resin produced by DuPont of Wilmington, Del. This combination of core and cover materials provides a ball that is virtually indestructible by golfers. Further, such a combination imparts a high initial velocity to the ball that results in improved distance. Because the materials of which the ball is formed are very rigid, solid balls generally have a hard “feel” when struck with a club. Likewise, due to their hardness, these balls have a relatively low spin rate, which provides greater distance.
At the present time, the wound ball remains the preferred ball of more advanced players due to its spin and feel characteristics. Wound balls typically have either a solid rubber or liquid center core around which many yards of a stretched elastic thread or yarn are wound. The wound core is then covered with a durable cover material such as a SURLYN or similar material or a softer cover such as balata or polyurethane. Wound balls are generally softer and provide more spin than non-wound balls, which enables a skilled golfer to have more control over the ball's flight and final position. Particularly, with approach shots into the green, the high spin rate of soft, wound balls enables the golfer to stop the ball very near its landing position.
A number of patents have been issued that are directed to modifying the properties of a conventional solid ball through alteration of the typical single core, single cover construction. This alteration results in a multilayer ball having a dual cover layer, dual core layer, and/or a ball having a mantle layer disposed between the cover and the core. The inventions disclosed in the prior art patents are directed towards improving a variety of golf balls physical properties that help determine “in-play” characteristics.
Several patents are directed towards improving the carry distance of such balls. For example, U.S. Pat. No. 4,863,167 relates to a three piece solid golf ball having increased flight distance, wherein the ball has a center portion and an outer layer formed from a rubber composition, wherein the outer layer is harder than the center portion and further contains a gravity-adjusting filler so as to impart a higher specific gravity to the outer layer than that of the center portion. U.S. Pat. No. 5,184,828 relates to a solid three-piece golf ball having improved rebound characteristics and carry distance while maintaining an adequate spin rate, wherein these characteristics are allegedly obtained by controlling the size of the polybutadiene inner core and outer layer as well as their specific gravity and hardness. According to the '828 patent, the key to obtaining the desired rebound characteristics is that the maximum hardness (42–62 Shore D) must be located at the interface between the core and the mantle and the hardness must then decrease both inwardly and outwardly. U.S. Pat. No. 4,714,253 is also directed towards a three-piece golf ball having an improved rebound coefficient. This golf ball has a core with a Shore C hardness of 57–80 in its center, but not more than 83 at a distance between 5–10 mm from its center and an outer layer with a Shore C hardness of 70–83.
Additionally, there are a number of patents directed towards improving the spin and feel of solid balls while maintaining the distance provided by the solid construction. For example, U.S. Pat. No. 5,072,944 discloses a three-piece solid golf ball having a center layer and an outer layer prepared from a rubber composition, wherein it is desirable that the center core layer is softer than the outer layer, the layers having a hardness (Shore C) of 25–50 and 70–90, respectively.
U.S. Pat. No. 4,625,964 relates to a solid golf ball having a polybutadiene rubber core of a diameter not more than 32 mm, a polybutadiene rubber intermediate layer having a specific gravity of lower than that of the core material, and a cover. U.S. Pat. No. 4,650,193 is directed towards a solid golf ball having a core comprising a central portion and an integral outer layer, wherein the core is a curable elastomer such as polybutadiene which is treated with a cure altering agent to soften an outer layer of the core, to produce a central layer with a hardness (Shore C) of greater than 75 and an outer layer with a hardness (Shore A) of less than 80.
U.S. Pat. No. 4,848,770 discloses a solid three-piece golf ball which includes a core of a highly filled synthetic rubber or polymeric material, an intermediate mantle of an unfilled synthetic rubber and a cover. The core and intermediate mantle have a hardness of between 50–95 Shore D. U.S. Pat. No. 5,002,281 is directed towards a three-piece solid golf ball which has an inner core having a hardness of 25–70 (Shore C), an outer shell having a hardness of 80–95 (Shore C) and a cover. Further, the specific gravity of the inner core must be greater than 1.0, but less than or equal to that of the outer shell, which must be less than 1.3.
The prior art discloses a variety of materials other than polybutadiene for use as intermediate layers. For example, U.S. Pat. No. 5,253,871 concerns a golf ball having a three-piece structure comprising an elastomer core, an intermediate layer of a thermoplastic material containing at least 10% of etheramide block copolymer, preferably blended with an ionomer, and a thermoplastic cover. U.S. Pat. No. 5,681,898 is directed to a multilayer golf ball having a conventional polybutadiene core, an ionomer cover and an intermediate layer formed from a blend of an ethylene methacrylic acid copolymer and a vulcanizate formed from polybutadiene and a peroxide curing agent.
U.S. Pat. Nos. 5,439,227 and 5,556,098 both disclose multilayer golf balls which have a conventional polybutadiene core, conventional covers and an intermediate layer formed from a polyetherester block copolymer blended with an ionomer.
Further, there are also several patents that are directed to golf balls having multiple cover layers. For example, U.S. Pat. No. 4,431,193 relates to a golf ball having a multilayer cover wherein the inner layer is a hard, high flexural modulus ionomer resin and the outer layer is a soft, low flexural modulus ionomer resin, and wherein either (or both) layers may comprise a foamed ionomer resin. U.S. Pat. No. 5,314,187 also relates to golf balls having a multiple layer cover, wherein the outer layer is molded over the inner layer and comprises a blend of balata and an elastomer and the inner layer is an ionomer resin. U.S. Pat. No. 4,919,434 is directed towards a golf ball having a cover which comprises an inner layer and an outer layer, each of which comprise a thermoplastic resin. Preferably the layers include materials that are capable of bonding with each other, for example, by heat, or by other means which are readily known to one of ordinary skill in the art.
U.S. Pat. No. 5,813,923 discloses a golf ball having a core and a cover with an intermediate layer having a flexural modulus of less than 10,000 psi. The core has a compression of less than 70 and the cover has a flexural modulus of greater than 75,000 psi.
However, none of the patents discussed above disclose the multilayer ball of the current invention that employs the materials, and has the improved golf ball properties, as disclosed herein.
It has now been discovered that the use of a polyurethane or polyurea composition, according to the present invention, in forming golf ball cores, intermediate layers, and/or covers, can raise the velocity of a golf ball prepared with the composition closer to the velocities observed with SURLYN®-covered golf balls. Additionally, the curatives used in the compositions of the present invention are less expensive than many curatives typically used by those of ordinary skill in the art, such as VERSALINK® P-250, an oligomeric diamine manufactured by Air Products and Chemicals, Inc. Moreover, the compositions of the present invention are less environmentally hazardous than other cost-effective options, such as ETHACURE® 300 and ETHACURE® 100.